Amelanotic melanoma in vivo and in vitro can be exceedingly difficult to identify with certainty. Melanosomes, when present by electron microscopy, are unique to this tumor. Frequently, however, atypical melanosomes or no cytoplasmic granules are present. In such cases, diagnosis and therapy are jeopardized by this ambiguity. This project is intended to define the limits of melanosome morphology unique to melanoma, and to corroborate this with formaldehyde-induced autofluorescence of the same tissue or culture.